Blasting cartridge or borehole charge



Sept. 26, 1939.

A. G. WHITE BLASTING CARTRIDGE OR BOREHOLE CHARGE Filed Feb. 17, 1936 2 Sheets-Sheet 1 INVENTOR.

ATTORN EY Sept. 26, 1939. A. 6. WHITE. 2,174,172

BLASTING CARTRIDGE OR BOREHOLE CHARGE Filed Feb. 17, 1936 2 Sheets- Sheet 2 %L5ER7 GREV/LLE WHUE INVENTOR ATTORNEY Patented Sept. 26, 1%39 Application February 17, 1936, Serial No. 64,381 in Great Eritain February 18, 1935 2 @laims.

This invention relates to blasting cartridges and borehole charges of the kind adapted to cause a relatively gentle heaving action and a relatively small shattering effect. Cartridges and borehole charges of this kind are particularly For example, a borehole charge of the kind described may comprise one or more cartridges of a low density explosive, such as may be made by mixing With'the other ingredients of the explosive a carbonaceous ingredient characterised by an unusually low density. The density of such an explosive, however, cannot be reduced much below 0.6 gm./c. 0. without detriment to the propagating efiiciency, while the manufacture of the low density explosive involves methods and/or ingredients.

the use of special 3 A number of methods of arranging the borehole charge have also been proposed in which, in order to obtain a low loading density, a part of the charge space in the borehole is left unoccupied. The practice of blasting-with part of the charge 9 space unoccupied by the blasting cartridge or cartridges is customarily described as cushion blasting.

Cushion blasting has been eflected by means of borehole charges consisting of cartridges of diameter substantially less than that of the borehole arranged in end to end contact and lying along the floor of the borehole in an eccentric position. A disadvantage of this method is that, if the diameter of the cartridges is much less than that of the borehole, the cartridges tend to form an irregular arrangement in the borehole, with consequent uncertainty and irregularity of propagation. It has been proposed to use cartridges having a diameter substantially less than that 1 of the borehole in association with devices or attachments for supporting the cartridges coaxially with the borehole.

In so far as this arrangement permits end to end contact over the full cross-sectional area of the cartridge, it does not cause, theoretically, a reduced efiiciency of propagation, but in practice it is found that the inconvenience of loading such an arrangement in the borehole, and the time required for assembling the borehole charge are considerable.

Annular cartridges of external diameter substantially equal to that of the borehole, and constructed with a hollow.axial space, have also been proposed, but such cartridges are relatively dimcult to manufacture and, if the axial space is of any considerable size, the efiiciency of propagation from cartridge to cartridge is not so good as in a file of solid cartridges of circular crosssectional area equal to that of the annular cartridge. Spacing members or devices have been inserted between blasting cartridges arranged in 19 file in a borehole, but longitudinal separation of adjacent cartridges in this manner also causes less efiicient propagation of detonation from cartridge to cartridge. Conical cartridges having a base adapted to fit the cylindrical borehole have 35 also been proposed, but the small area of contact between the apex of one cartridge and the base of the next gives a lower efilciency of propagation than normal arrangement of cylindrical cartridges of uniform, cross-section.

An object of the present invention is the provision of improved cartridges suitable for cushion blasting, consisting of any convenient normal or low density explosive, which can be assembled. in the borehole rapidly and with certainty and 25 without the aid of spacing or positioning devices to form a. borehole charge characterised by efficient propagation from cartridge to cartridge.-

According to the invention cartridges suitable for cushion blasting comprise any convenient 30 normal or low densityexplosive and are so formed as to have a non-circular solid cross-section uniform throughout the length of the cartridge, of area substantially less than the area of the cir-. cumscribing circle, and such that the minimum 35 end contact ratio as hereinafter defined is not 1 less than 50%. The cartridges are adapted to be loaded into a borehole having a cross-section the same. as that of the circumscribing circle. It will be understood that the ratio of the area of cross- 41,4

section of the cartridge to that of the circumscribing circle is a measure of the loading density of the assembled borehole charge.

- The term minimum end contact ratio as used above and in the appended claims will be underas stood from the following considerations.

The cartridges of the present invention, when loaded in a borehole, are so located with respect to the borehole that there is no risk of lateral displacement. Successive cartridges in file may, 50 however, take up any random rotational orientationwith respect to adjacent cartridges. In order to ensure efflcient propagation, it is desirable that there should be a column of explosive continuous between adjacent cartridges and having as large -not less than 50% as already described;

a diameter as possible, and hence successive cartridges should, for all rotational orientations,

have a relatively large cross-section in 'end-to-end contact. If two cartridges oi the present invention are arranged end-to-end in a borehole, and one is then rotated with respect to the other, the area of common contact will have a maximum value when the two cartridges are similarly oriented, and will pass through one or more minimum values as the cartridge is rotated through a complete revolution. The ratio of the absolute minimum value to the total cross-sectional area of the cartridge is termed the minimum end contact ratio.

The preferred form of cartridge is that in which the area of the cross-section is not more than two-thirds of that of the circumscribed circle. Thus in the preferred form of the inventioii the cross-section is an equilateral triangle, and in this form the loading density is 41%, and the minimum end contact ratio is 66%%; A cartridge of square cross-section may also be used according to the invention, the cartridge having a greater minimum end contact ratio, namely, 80%, but also a higher loading density, namely, 64%. It will he understood that the cross-section of the cartridges need not be rectilinear; for example, cartridges of elliptical cross-section may be i'ormed with a suitable loading density and corresponding minimum end-contact ratio.- The longitudinal edges of vtriangular prismatic cartridges may also be rounded off slightly.

The cartridges according to the present invention may be illustrated more clearly by reference to the accompanying drawings. Figure 1 is a graph in triangular coordinates and relates to the proportions of a triangular cartridge. Figure 2 is a view in vertical section of a borehole charge comprising a plurality of cartridges of triangular cross-section disposed in acylindrical borehole.

Cartridges of triangular cross-section fall within the scope of the present invention provided that the minimum end contact ratio is The effect of variations in the shape oi! the triangle on the minimum end contact ratio is illustrated on the accompanying graph in triangular coordinates, but the invention is not limited by this graph and is defined solely in the appended claims.

In this graph: any point represents on the triangular coordinates the magnitudes A, B and C of the three angles of a triangle. It will be understood that any angle'oi a given triangle may be chosen as the angle A and either of the remaining angles as the angle B, and consequently there will be in general six points on the drawing representing the same triangle. The symmetrical figure disposed near the center of the area bounded by the triangular coordinates in this drawing illustrates the area within which all points represent triangles having a minimum end contact ratio 0! more than 3 50%. The centre point represents an equilateral triangle.

The cartridges 0! the present invention may suitably be formed by loading powder explosives into cases of the desired form, or by pressing them into pellets in suitable dies. Plastic explosives may be extruded irom a suitably shaped nozzle, or a cylindrical rod' extruded from a nozzle of .the usual form may be passed between rolls provided with grooves adapted to give the plastic explosive the desired cross-section. Cartridges 0! the desired form may also be stamped out of a block of explosives by means of a honeycomb or other suitable form of cutting device, so that little or no waste explosive is formed during the cutting operation.

An advantage of the use of cartridges of. the preferred equilateral triangular cross-section is that they can be formed without waste and packed with no free space in the packed ar v 'rangement, thus ensuring economy and safety in packing and transport.-

A further advantage of the cartridges 0! the preferred shape is that they will not scoop up loose stone or coal dust when pushed into a,

borehole, but will allow small loose impediments to remain undisturbed in the clearance space. In this manner a frequent cause 01 failure in propagation, i. e., the separation of cartridges in flle by loose fragments or dust present in the borehole, is avoided.

I claim: e 1. An explosive cartridge suitable for cushion blasting, consisting of a detonating explosive charge of triangular cross-section substantially uniform throughout the length or said charge and such that the ratio of the minimum possible area of common end contact to the total crosssectional area 01' said charge is not less than 0.50 when two cartridges containing said charges I are placed end-to-end along a common axis.

2. The cartridge of claim 1 wherein'the loading density is between 41% and 65%.

ALBERT GREVJLLE WHITE. 

